The invention relates to quantum electronics, specifically to high-power multimode, monomode, and/or single-frequency radiation sources, and in particular to semiconductor optical amplifiers.
Traditionally, a semiconductor optical amplifier (SOA) consists of a master source of input radiation whose output is optically coupled by an optical system to the input of an amplifying component (AC). See S. O""Brien et al., IEEE J. of Quantum Electronics (1993), Vol. 29, No. 6, pp. 2052-2057, and J. P. Donnelly et al., IEEE Phot. and Technology Letters (1996), Vol. 8, pp. 1450-1452). The optical signals usually are spontaneous, superluminescent, or laser radiation. By virtue of the specific features of a SOA, such as small size, high gain per unit length, high efficiency, potentially low cost, integrability into optoelectronic circuits, etc., the SOA unquestionably has great prospects for use both in the design of complex communications networks, particularly branched networks, and in the development of efficient high-power radiation sources.
An SOA in a discrete implementation is known that includes a master source of input radiation that is input, when the amplifier is in operation, at an input angle xcex4 into an AC optically coupled to the source. See L. Goldberg et al., IEEE J. of Quantum Electronics (1993), Vol. 29, No. 6, pp. 2028-2042. The AC is implemented on the basis of a semiconductor laser heterostructure that contains an active layer with a refractive index na and a bandgap Ea (eV) positioned between two cladding layers, in each of which there is at least one sublayer. The active gain region is implemented by using barrier regions to form a mesa strip that widens linearly from its initial width Win of 10 xcexcm at the input face of the active gain region, to a final width Wout of 160 xcexcm at the output face of the active gain region. The length LAGR of the SOA was 1500 xcexcm. Note that the longitudinal axis of the active gain region, which lies in the active layer and is the optical gain axis of the AC, is located on the same optical axis as that of the master source and the optical system. The method of inputting the input radiation into the active gain region and of outputting radiation therefrom after amplification are via an optical facet on the input face of the active gain region and an optical facet on the output face of the active gain region. These optical facets are conditionally referred to as first optical facets and have antireflective coatings applied whose reflection coefficient, R, was in this case Rxcx9c0.003. The first optical facets are positioned at angles of inclination "psgr"1 and "psgr"2 to the plane perpendicular to the optical gain axis, which is referred to as the normal plane. L. Goldberg et al., in IEEE J. of Quantum Electronics (1993), Vol. 29, No. 6, pp. 2028-2042, discloses a device wherein the first optical facets of the AC are parallel to the normal plane. The sizes of the input and output apertures for the AC discussed by L. Goldberg et al. in IEEE J. of Quantum Electronics (1993), Vol. 29, No. 6, pp. 2028-2042 are:
Sin=dAGRWin,xe2x80x83xe2x80x83(1)
and
Sout=dAGRWout,xe2x80x83xe2x80x83(2)
respectively, where dAGR is the thickness of the active gain region, which usually does not exceed 1 xcexcm. Accordingly, for the AC of the SOA disclosed by L. Goldberg et al. in IEEE J. of Quantum Electronics (1993), Vol. 29, No. 6, pp. 2028-2042, Sin is no more than 10 xcexcm2 and Sout is no more than 160 xcexcm2.
Antireflective coatings applied to the first optical facets of the active gain region are used as a means of suppressing spurious reflections and rereflections of the output signal (SPPI) in the AC shown by L. Goldberg et al. in IEEE J. Of Quantum Electronics (1993), Vol. 29, No. 6, pp. 2028-2042.
The SOA disclosed by L. Goldberg et al., IEEE J. Of Quantum Electronics (1993), Vol. 29, No. 6, pp. 2028-2042 uses as its master source of input radiation a master laser diode with monomode radiation and a power PMSout of 100 mW. The input radiation was focused by the optical system into a spot measuring 1xc3x974 xcexcm on the first (input) optical facet. In addition, the input beams were input into the active gain region at different input angles xcex4. This resulted in the input into the amplifying component of an input power Pin in the AC of 25 mW through the first face of the active gain region.
When an operating current Iwork of 3 A was passed through the AC with a length LAGR of 1500 xcexcm that was disclosed by L. Goldberg et al., in IEEE J. Of Quantum Electronics (1993), Vol. 29, No. 6, pp. 2028-2042, 2.5 W of amplified output radiation power, Pout, was obtained. The input aperture was no larger than 1 xcexcm. In the vertical plane, the angle of divergence xcex8xe2x8axa5 as with the usual injection-type emitters, was large, i.e., approximately 35xc2x0. By vertical plane is meant a plane that passes through the longitudinal axis of the active layer and that is perpendicular to the layers of the laser heterostructure. The output aperture was small, i.e., no more than 1 xcexcm. The effective angle of divergence xcex8∥ of the output radiation in the horizontal plane was 0.29xc2x0, which corresponds to the diffraction-limited divergence for the indicated aperture size of 160 xcexcm. By horizontal plane is meant the plane that is perpendicular to the vertical plane and that passes through the normal of the amplified output radiation front is called horizontal plane. In the known AC in question, the horizontal plane corresponds to the plane of the active layer.
One preferred embodiment of the present invention comprises a semiconductor optical amplifier comprising a master source of input radiation and an amplifying component optically coupled to the master source. The amplifying component comprises a semiconductor heterostructure that includes an active layer positioned between two cladding layers and an ohmic contact formed to at least one sublayer of the semiconductor heterostructure. The amplifying component also includes an input-output region comprising at least one additional layer on at least one side of the heterostructure. This additional layer adjacent to the heterostructure comprises one or more sublayers having refractive indices nIORq and optical loss factors xcex1IROq (cmxe2x88x921), where q=1, 2, . . . , p are integers corresponding to the sublayers of the radiation input-output region sequentially counted from their boundaries with the heterostructure,
In the semiconductor optical amplifier, the input-output region is adapted to receive input radiation at an angle of input, xcex4. Additionally, the angle of the input radiation and the net loss factor xcex1OR (cmxe2x88x921) for the amplified radiation flowing from the active layer are such that       0     less than           arccos      ⁢              xe2x80x83            ⁢                        n          eff                          n          IOR1                      ≤          arccos      ⁢              xe2x80x83            ⁢                        n                      eff            ⁢                          -                        ⁢            min                                    n          IOR1                      ,            and      ⁢              xe2x80x83            ⁢              n                  eff          ⁢                      -                    ⁢          min                       greater than           n      min        ,
where neff is the effective refractive index of the heterostructure in aggregate with the radiation input-output region, and NIOR1 is the refractive index of the radiation input-output region, neff-min is the minimum value of neff out of all possible neff for the multiplicity of heterostructures that are of practical interest, in aggregate with radiation input-output regions, and nmin is the smallest of the refractive indices of the layers of the heterostructure.